1. Technical Field
This disclosure relates to orthodontic appliances, including archwires and associated orthodontic brackets.
2. Description of Related Art
Orthodontic appliances are commonly used to correct misaligned teeth.
There are many types of orthodontic appliances. However, each may have drawbacks, such as requiring too much time to prepare and/or install.
One type of orthodontic appliance is the pin and tube appliance. The pin and tube appliance can control the movement and position of each tooth in three-dimensional space. It can include an orthodontic archwire with a male “pin” that inserts into a female vertical “tube” that is attached to the tooth. The pin and tube do not move relative to each other. Interproximal loops can be placed in between the teeth to move the teeth to open or close spaces.
However, the pin and tube appliance can present challenges, including:                Custom bends and interdental loops may have to be bent manually in the archwire for the pins to fit into the vertical tubes and for the archwire to move the teeth to the desired location. This process may need to be performed manually by a human and may be very demanding and tedious.        The male pin may need to be soldered onto the orthodontic archwire with a needed inclination. As the teeth move, the pins may need to be unsoldered and re-soldered to new locations. This may also be a very demanding and tedious manual process.        The solder joint between the male pin and orthodontic archwire may break.        The orthodontic archwire may be difficult to insert and remove from the patient because the locking mechanism may require bending the male insert over the tube to lock and un-bending the male insert from the tube to unlock.        Stainless steel wires may be needed. Because of elastic limitations of stainless steel, many different size wires with different properties may need to be used for each case. The may complicate wire bending, pin soldering, and locking, and unlocking procedures when changing wires.        The device may be ineffective in dealing with axial rotations of teeth.        
Another type of orthodontic appliances is the edgewise appliance. An edgewise appliance may include orthodontic brackets (with rectangular slots) that are bonded onto each tooth. An archwire that is rectangular in cross-section may fit into rectangular slots in the orthodontic brackets.
However, the edgewise appliance can present problems, including:                It may require significant custom wire bending along three axis (or three orders) due to differences in tooth size and tooth position. These axis may include in-out (first order bend), up-down (second order bend), and faciolingual inclination (3rd order bend).        The wire may need to be tied to an orthodontic edgewise orthodontic bracket. This can be time consuming, especially if the brackets are behind the teeth, also known as lingual braces.        Sliding the archwire with respect to the orthodontic bracket can require application of external forces. Frequent appointments may be required to ensure that these external forces do not overcorrect or under-correct the amount of desired movement.        This system may depend heavily on sliding between the orthodontic bracket and archwire to move teeth. However, the amount of sliding that can be achieved can be difficult to predict due to the unpredictable nature of the amount of friction to overcome. This can again require frequent monthly appointments to ensure that the tooth moves in the desired amount.        
Another type of orthodontic appliances is the pre-adjusted, straight-wire appliance that uses nickel-titanium wires. This appliance can minimize the amount archwire bending that is required in edgewise appliances. The shape memory, super-elasticity, and lower modulus of elasticity features of shape memory alloys can lower the amount of force delivered to the teeth and significantly reduce the pathologic lesions as a result of heavy force use from rigid stainless steel wires. The large range of movement for some of shape memory alloy archwires can reduce the number of archwires required for treatment and, as such, reduce the number of activation appointments that are needed.
However, the pre-adjusted straight-wire appliance can present challenges. For example, considerable time may be required to tie the archwire into the orthodontic bracket, especially when lingual braces are used. The appliance may also still rely heavily on sliding the orthodontic bracket relative to the archwire to open and close space. To overcome the unpredictable amount of friction that is generated, frequent monthly appointments may still be required to ensure that the correct amount of movement is achieved.
Another type of orthodontic appliance uses self-ligating orthodontic brackets. These may reduce the amount of time and effort required to tie a wire into an orthodontic straight-wire appliance. Various types of doors and latches may be provided to replace tying the orthodontic wire. These doors and latches can make it easier to deliver and change orthodontic archwires. They can also eliminate the unnecessary tying and untying of archwires at appointments when the archwire does not need to be changed. Self-ligating orthodontic brackets can also provide a metal-to-metal interface between the orthodontic slot and the wire, reducing the amount of friction when moving teeth.
However, self-ligating orthodontic brackets can present problems, including:                Self-ligating orthodontic brackets can sacrifice torque control of the teeth because of a high degree of orthodontic slop that can be present between the orthodontic slot and the archwire.        Self-ligating orthodontic brackets may rely heavily on sliding the orthodontic bracket relative to the archwire to open and close space. Thus, frequent monthly appointments can still be required to ensure that the correct amount of movement is achieved.        Self-ligating orthodontic brackets can be bulkier than other types of orthodontic brackets. This can make control of the teeth much more difficult when using the orthodontic brackets on the lingual surface (behind the teeth) because there may be less interdental space between the orthodontic brackets, resulting in a much more rigid wire that can be harder to control.        Self-ligating orthodontic brackets can have several moving parts that can break under wear from occlusal forces in the mouth or from normal use of the appliance.        
CAD/CAM technology can also be used in connection with orthodontics. This technology can be used to create an expected desired end result prior to the starting of orthodontic treatment. Customized wires and orthodontic brackets can be designed based on the expected desired end result of the orthodontic treatment to reduce the amount of doctor intervention required at each appointment.
However, using CAD/CAM technology may not overcome all of the problems associated with the orthodontic appliances, such as:                These customized appliances can rely heavily on sliding the orthodontic bracket relative to the archwire to open and close space. Thus, frequent appointments may still be required to ensure that adequate force is delivered to achieve sufficient tooth movement.        Customized orthodontic brackets can also be difficult to tie in, especially when placed on the lingual surface of the teeth.        Customized self-ligating orthodontic brackets can be bulky, difficult to control, and damage prone.        